Certain findings on chest x-rays (see the section, “How Is Malignant Mesothelioma Diagnosed?”) that suggest asbestos exposure could prompt the need for further tests or close follow-up. However, the chest x-ray is not an effective test for early detection of mesothelioma in the general population. One test being studied is a blood test that measures the levels in the blood of osteopontin, a protein that is elevated in people who have lung damage due to asbestos. It is even higher if a person develops mesothelioma.

In all cases, the diagnosis of mesothelioma must first be unquestionably established by biopsy of affected or suspicious tissues, and by definitive microscopic examination by a trained pathologist. Biopsy almost always requires an invasive procedure such as thoracoscopy and pleural biopsy, or laparotomy or laparoscopy, The removed tissues may be treated with special biological or chemical stains which are used to help the pathologist establish a firm diagnosis. The pathologist usually also comments upon the rate of growth and biological virulence of the tumor.

Second, the tumor must be staged if possible by X-ray, CAT scan, MRI or other types of scans to clarify its location within the body, and to estimate the likelihood of effective curative or palliative therapy. Staging of mesothelioma by x-ray measurements, however, is difficult and often unreliable.